Off the Menu
On Rosh Hashanah it is customary not to eat sour or bitter foods, e.g., pickles or horseradish. This symbolizes that we shouldn't have a “sour” year but rather a sweet one. Drinking hard liquor is acceptable (in moderation obviously).
It is also customary to refrain from eating nuts as eating nuts increases one's saliva which may disturb one's concentration in prayer. In addition, the Gematriyah (numerical value) of Egoz /nut is 17, the same numerical value as Chet/sin (not counting the “alef” which is not vocalized). Some refrain from eating these foods until after Hoshana Rabbah.